Robot control apparatus, and method and program for obtaining angle of joint of robot

Abstract

In a method of obtaining an angle of each joint of a 6-axis vertical articulated robot when a position and a posture of an end effector attached on a sixth axis are given, a predetermined amount of offset exists between a sixth axis and a fourth axis, and the method includes sequentially determining a point of interest, which is a point on a circumference of a circle having the predetermined amount as a radius, around a first intersection point, on a plane which includes the first intersection point which is an intersection point of the sixth axis and the fifth axis and the plane which is orthogonal to the sixth axis, calculating a second intersection point, which is an intersection point of the fourth axis and the third axis, when it is assumed that the point of interest is an intersection point of the fifth axis and the fourth axis, calculating an inner product value of a first vector directed from the calculated second intersection point to the point of interest and a second vector directed from the point of interest to the first intersection point, and estimating that the point of interest, when an absolute value of the inner product value is less than or equal to a predetermined threshold, is an intersection point of the fifth axis and the fourth axis.

What is claimed is: 
     
       1. A robot control apparatus for obtaining an angle of each joint of a 6-axis vertical articulated robot when a position and a posture of an end effector attached on a sixth axis are given, wherein, in the 6-axis vertical articulated robot, the sixth axis of a sixth joint and a fifth axis of a fifth joint perpendicularly intersect each other, the fifth axis and a fourth axis of a fourth joint perpendicularly intersect each other, the fourth axis and a third axis of a third joint perpendicularly intersect each other, and there is a predetermined amount of offset between the sixth axis and the fourth axis, the robot control apparatus comprising:
 determination circuitry to sequentially determine a point of interest, which is a point on a circumference of a circle having the predetermined amount of offset as a radius, around a first intersection point, on a plane which includes the first intersection point which is an intersection point of the sixth axis and the fifth axis and the plane which is orthogonal to the sixth axis; 
 a first calculation circuitry to calculate a second intersection point, which is an intersection point of the fourth axis and the third axis, when it is assumed that the point of interest is an intersection point of the fifth axis and the fourth axis; 
 a second calculation circuitry to calculate an inner product value of a first vector directed from the second intersection point calculated by the first calculation circuitry to the point of interest and a second vector directed from the point of interest to the first intersection point; and 
 estimation circuitry to estimate that the point of interest, when an absolute value of the inner product value is less than or equal to a predetermined threshold, is an intersection point of the fifth axis and the fourth axis; 
 wherein the sequentially determination of the point of interest, the calculation of the second intersection point, the calculation of the inner product value of the first vector, and the estimation that the point of interest is the intersection point of the fifth axis and the fourth axis are all performed in real-time. 
 
     
     
       2. The robot control apparatus of  claim 1 , wherein
 the determination circuitry, the first calculation circuitry, the second calculation circuitry, and the estimation circuitry are defined by a controller. 
 
     
     
       3. A method of obtaining an angle of each joint of a 6-axis vertical articulated robot when a position and a posture of an end effector attached on a sixth axis are given, wherein, in the 6-axis vertical articulated robot, the sixth axis of a sixth joint and a fifth axis of a fifth joint perpendicularly intersect each other, the fifth axis and a fourth axis of a fourth joint perpendicularly intersect each other, the fourth axis and a third axis of a third joint perpendicularly intersect each other, and there is a predetermined amount of offset between the sixth axis and the fourth axis, the method comprising:
 sequentially determining a point of interest; which is a point on a circumference of a circle having the predetermined amount of offset as a radius, around a first intersection point, on a plane which includes the first intersection point which is an intersection point of the sixth axis, and the fifth axis and the plane which is orthogonal to the sixth axis; 
 calculating a second intersection point which is an intersection point of the fourth axis and the third axis when it is assumed that the point of interest is an intersection point of the fifth axis and the fourth axis; 
 calculating an inner product value of a first vector directed from the second intersection point to the point of interest and a second vector directed from the point of interest to the first intersection point; and 
 estimating that the point of interest, when an absolute value of the inner product value is less than or equal to a predetermined threshold, is an intersection point of the fifth axis and the fourth axis; 
 wherein the sequentially determining the point of interest, the calculating the second intersection point, the calculating the inner product value of the first vector, and the estimating that the point of interest is the intersection point of the fifth axis and the fourth axis are all performed in real-time. 
 
     
     
       4. A non-transitory computer-readable medium containing a computer program that causes a computer to perform a method of obtaining an angle of each joint of a 6-axis vertical articulated robot when a position and a posture of an end effector attached on a sixth axis are given, wherein, in the 6-axis vertical articulated robot, the sixth axis of a sixth joint and a fifth axis of a fifth joint perpendicularly intersect each other, the fifth axis and a fourth axis of a fourth joint perpendicularly intersect each other, the fourth axis and a third axis of a third joint perpendicularly intersect each other, and there is a predetermined amount of offset between the sixth axis and the fourth axis, the method comprising:
 sequentially determining a point of interest, which is a point on a circumference of a circle having the predetermined amount of offset as a radius, around a first intersection point, on a plane which includes the first intersection point which is an intersection point of the sixth axis and the fifth axis and the plane which is orthogonal to the sixth axis; 
 calculating a second intersection point which is an intersection point of the fourth axis and the third axis when it is assumed that the point of interest is an intersection point of the fifth axis and the fourth axis; 
 calculating an inner product value of a first vector directed from the second intersection point to the point of interest and a second vector directed from the point of interest to the first intersection point; and 
 estimating that the point of interest, when an absolute value of the inner product value is less than or equal to a predetermined threshold, is an intersection point of the fifth axis and the fourth axis; 
 wherein the sequentially determining the point of interest, the calculating the second intersection point, the calculating the inner product value of the first vector, and the estimating that the point of interest is the intersection point of the fifth axis and the fourth axis are all performed in real-time.